84 AN INTRODUCTION TO THE STUDY OF VIRUSES 
In the second method, the virus-containing fluids were removed 
from the eggs, formaldehyde was added and the whole spun in a 
Sharples supercentrifuge. The sedimented virus was then re-suspended 
in salt solution and administered by sub-cutaneous injection about 
#y of a milligram of virus constituting a dose. This represents about 
half the material obtained from the fluids of a single chick embryo. 
Since there is no cross-immunity between the two main strains of 
influenza virus, A and B, the vaccine to be effective must be a mixture 
of both strains of the virus. 
As Wilson Smith (1939) has pointed out, the value of serum therapy 
in virus diseases is very limited and he suggests that the intra-cellular 
habitat of the parasite may largely explain why an antiserum is of 
little use once the disease has been established. 
Since the serum of a recently recovered or artificially immunized 
animal contains antibodies which are capable of neutralizing the 
specific virus, serum-virus mixtures can be prepared which are 
completely non-infective. In some cases, mixtures are used where the 
amount of serum is insufficient to inactivate all the virus; a mild attack 
of the disease can then be induced which will give rise to a solid 
immunity. 3 
Another method which has been used against cattle plague and 
dog distemper is to inoculate the virus on one side of the animal and 
then, after a brief interval to allow the virus to gain a foothold, 
inoculate the serum on the other side. 
The story of inoculation against measles is an intriguing one and 
the following account is based largely on Lauffer’s (1946) description 
of it. From studies on the composition of human blood carried out 
during the past twenty years, it has been discovered that the fluid 
component consists mainly of five proteins, albumin, fibrinogen, 
alpha-globulin, beta-globulin, and gamma-globulin. Furthermore, 
it was discovered that the antibodies to diseases are generally associated 
with the gamma-globulin fraction. The increasing use of blood 
transfusion, especially for the treatment of shock, led to the discovery 
that the constituent of blood most effective for the purpose is serum 
albumin. It is from these fractionating procedures that the inoculation 
treatment of measles finally arose. During the war, large stocks of 
human blood were accumulated, especially in the U.S.A., and the 
question naturally arose whether those fractions of the blood not 
needed for blood transfusion could not be put to some other useful 
purpose. Since such a large proportion of adult human beings are 
